1. Field of the Invention
The present invention relates to a continuously variable transmission that continuously varies the rotation speed of the input shaft and transmits the speed to the output shaft by using a traction drive using traction force, and more particularly relates to a continuously variable transmission that continuously varies the speed using conical planetary rollers.
2. Description of the Related Art
As shown in FIG. 1, a conventional continuously variable transmission that includes an input shaft 3 and an output shaft 4 rotatably supported via bearings 2 on flanges 1a connected to both sides of a cylindrical housing 1, a sun roller (inner wheel) 5 in the shape of the frustum of a cone connected to the input shaft 3 using a key 3a so that the sun roller 5 rotates integrally with the input shaft 3, a holder 6 rotatably supported via a bearing 3b on the input shaft 3, a plurality of tapered rollers (planetary rollers) 7 rotatably supported on the holder 6 that roll on the outer peripheral surface of the sun roller 5, an output ring (follower outer wheel) 8 that rotates integrally with the output shaft 4 and contacts the outside of the tapered rollers 7, a speed change ring (rotationally fixed outer wheel) 9 that contacts the outside of conical portions 7a integrally provided on the tapered rollers 7 and that can only be driven reciprocally in the direction of the generating lines of the conical portions 7a, and so on, is known. See, for example, Japanese Patent Application Laid-open No. H6-280961.
In this continuously variable transmission, when the input shaft 3 rotates, the sun roller 5 rotates integrally with it, the tapered rollers 7 that contact the outside of the sun roller 5 rotate and revolve, the output ring 8 rotates as a result of the rotation of the tapered rollers 7, the output shaft 4 that is integral with the output ring 8 rotates, and the rotation speed of the output shaft 4 is increased or decreased in accordance with the position of the speed change ring 9.
However, in this continuously variable transmission, the normal load at the contact surface of the tapered rollers (planetary rollers) 7 and the sun roller 5, the normal load at the contact surface of the tapered rollers 7 and the output ring 8, and the normal load at the contact surface of the conical portions 7a of the tapered rollers 7 and the speed change ring 9 depends on the initial assembly accuracy. Also, there is no means of correcting the variation in the normal loads due to changes with time, and the like. Therefore it may not be possible to obtain the necessary traction force, and there is a possibility that the speed change effect will not be reliably obtained. In particular, the tapered rollers 7 are supported cantilevered from the holder 5, so the conical portions 7a of the tapered rollers 7 can be easily bent, so it is difficult to greatly increase the contact force with the speed change ring 9.
Also, a thrust load is generated in the direction of the axes of the input shaft 3 and the output shaft 4 as the normal loads increase, and this thrust load is received by the bearings 2 of the input shaft 3 and the output shaft 4 or the housing 1. Therefore, the bearings 2 and the housing 1 deform with time, or the temperature of the lubricating oil rises due to heat in the area around the bearings, and so on, so there is the danger of wear and reduction in power transmission efficiency, and so on. On the other hand, if the stiffness of the housing 1 is increased as a measure against deformation, this will cause the size or weight to increase.